Noise and streaks due to photon starvation can seriously corrupt the quality of X-ray CT images. Although an increased dose of X-ray may alleviate the problem, it is not clinically acceptable for patient safety. To achieve diagnostically useful image quality at a safe dosage level, prior art attempts have sought for decades a desirable solution for substantially reducing noise and streaks. With an elevated awareness of low doses, the above described research filed has recently gained great importance and received serious attention.
To improve results, prior efforts have utilized adaptive filters in lieu of fixed filters. Some examples of the fixed filters include a triangular filter and a bilateral filter. Similarly, some examples of the adaptive filters include an adaptive Gaussian filter and an adaptive trimmed mean filter. Among the prior art adaptive filters, the filter parameters still need to be adjusted for the same type or set of projection data, and the adjustment relies on an empirical and or ad hoc optimal. In another exemplary filter, the variance of a Gaussian filter kernel is the same as the noise variance of the data. Due to the ad hoc nature, the above described prior art adaptive filters insufficiently reduce noise and or streaks.
It remains desired to have an effective filter to maximize the noise and streak reduction while its filter parameters are not adjusted in a complex or ad hoc manner.